The present invention relates to an improved treatment of sewage solids, sand, rubbish and similar solid matter of more or less big particle consistency, to which organic substances adhere, which are filtered out at more or less high proportions of a solid-liquid mixture and are removed, especially dumped or incinerated, whereas the residual liquid correspondingly more or less freed of solids is preferably passed to a biological waste water treatment system (clarification plant).
In waste water treatment systems, the first treatment stage is a so-called mechanical treatment stage which, as rule, consists of a so-called rake or screen system and a sand catcher.
It is known to lift solids out of a raceway (particularly one of a bigger size) with the aid of rake conveyors and to discharge the solids into containers or comminutors. It is further known (especially with narrow raceways) to use sieve filter means with an associated conveying worm which then pass the solids discharged from the raceway to a container or subsequent treatment system.
Finally, it is known to generally comminute and squeeze the accumulating solids, for example, by means of a comminution pump or centrifugal device.
Solids which have settled in the sand catcher are normally conveyed by means of pumps or similar apparatus to a sand container or a so-called sand classifier.
This mechanical sewage treatment stage, of whatever type it may be, is followed by a biological waste water treatment system (clarification works) serving to decompose organic substances, i.e. the process which takes place there operates with organisms decomposing the organic substances.
Solids (rakings, sievings or sand) filtered out by the mechanical sewage treatment stage, but also substances not carried along with waste water, such as rubbish, contain many organic components. At present, these organic components mostly end up at the dump or incineration plant, along with the rakings, sievings, sand or rubbish. This is harmful and should be avoided.